1. Field of the Invention
The present invention relates to a manufacturing method for a piezoelectric body having an ABO3 perovskite oxide crystal film, a piezoelectric element using a piezoelectric body obtained by the manufacturing method, and a liquid discharge head.
2. Description of the Related Art
A piezoelectric body has a piezoelectric property for reversible transformation between electrical energy and mechanical energy. Specifically, the electrical energy is transformed into mechanical displacement, stress, or vibration, and then transformation reverse to this is performed. There is known a piezoelectric element obtained by utilizing the piezoelectric property. According to the piezoelectric property, if the piezoelectric body is formed into a thin film and an electric field is applied between a pair of electrodes sandwiching the piezoelectric body, the piezoelectric body causes displacement, and is restored if the electric field is removed therefrom. Depending on bending displacement to be generated, the piezoelectric element is classified into a uni-morph type, a bi-morph type, and the like. Specifically, those piezoelectric elements are used for various oscillators or radiators such as a motor which requires a reciprocating operation, an ultrasonic motor, a transducer, an actuator, an ink jet head, a microphone, and a sounding body (such as a speaker), various sensors in the field of biotechnology, medicine, and the like, an acceleration sensor for an automobile, a pressure sensor for measurement, and the like. Particularly, because of an excellent printing performance, simple handling, low costs, and the like, the piezoelectric element having the piezoelectric body utilizing a pressure wave is used in many cases for ink discharge of an ink jet head applied to a printing apparatus for a personal computer or the like. In the ink jet head using the piezoelectric element, for example, multiple individual liquid chambers each containing ink and communicating with a common liquid chamber are provided, displacement of the piezoelectric elements that are provided so as to correspond to the individual liquid chambers is transferred through a diaphragm, and the ink provided inside thereof is ejected as liquid droplets.
In recent years, while a color ink jet printer has been widely used, in addition to a demand for improvement of the printing performance, in particular, higher resolution and high-speed printing, there is another demand for increase in length and reduction in costs. Accordingly, with a structure of a multi-nozzle head having individual liquid chambers miniaturized, achievement of the higher resolution and high-speed printing has been attempted. In order to miniaturize the individual liquid chambers of the liquid jet head, it is necessary to achieve miniaturization, higher density, and higher performance of the piezoelectric element. In order to achieve increase in length and reduction in costs of the liquid jet head, it is necessary to enlarge an area of a substrate used for manufacturing the liquid jet head.
Up to now, the piezoelectric body used for the piezoelectric element is manufactured as, for example, a PZT-based ceramic oxide film by sintering a green sheet obtained by forming powdered paste of PbO, ZrO2, and TiO2 into a sheet shape. However, it is difficult to form the PZT-based ceramic oxide film with a thickness of, for example, 10000 nm or less by employment of that method. The green sheet is sintered at a temperature of 1000° C. or more, so the green sheet is shrunk to about 70% of its original length. It is impossible to apply the method of producing the piezoelectric body using the green sheet to production of the piezoelectric element for ink discharge of the ink jet head which is required to be positioned with a dimensional accuracy of an order of several micrometers.
Further, as a method of producing the piezoelectric body used in manufacturing the piezoelectric element, there is reported a method of producing a ceramic thin film having a thickness of 10000 nm or less by employment of a sputtering method, a CVD method, an MBE method, a sol-gel method, or the like. Those methods of producing the ceramic thin film are classified roughly into two types. One of them is a method of obtaining a desired crystalline thin film by epitaxial growth with the heating deposition (heating deposition method). Another one is a method, which is disclosed in Japanese Patent Application Laid-Open No. 06-171939, of obtaining a crystalline thin film by application of energy from an outside by thermal sintering, application of light, or the like after an amorphous film serving as a precursor of a crystal film is formed (post-annealing method).
In a case where the piezoelectric body is produced by the above-mentioned heating deposition method, a state where constituent atoms in interfaces between, for example, a substrate and a lower layer such as a lower electrode are scattered, or local projection of atoms of the lower layer occurs. For example, by observation using a transmission electron microscope (TEM), local projection of platinum used for the lower electrode, or interdiffusion of the constituent atoms have been found. It has been recognized that the local projection of the lower electrode is caused due to high-temperature heating at the time of production of the piezoelectric body. With regard to the interdiffusion of the constituent atoms, there is a fear that, in the vicinity of the interface with the lower layer, deviation from an original stoichiometric composition is generated, and another compound is formed of elements dissipated from the piezoelectric body. Therefore, a piezoelectric element having a foreign matter layer incorporated therein is produced separately from a piezoelectric element having a layer structure originally intended, which leads to significant deterioration of the piezoelectric property.
On the other hand, in a case where the piezoelectric body is produced by the post-annealing method, crystalline nuclei are randomly generated everywhere in a film during a process of transition from an amorphous film to a crystal film. Therefore, it is extremely difficult to control a crystal orientation property. Further, there arises a problem in that the piezoelectric body has high density, and an in-plane stress of the film becomes extremely large, which disturbs the piezoelectric property itself and deteriorates the adhesion between the film and the lower layer. It is impossible to use the piezoelectric element including the piezoelectric body as a piezoelectric element of the ink jet head which requires high adhesion between the piezoelectric layer and the lower layer with respect to the stress of reciprocating drive, and excellent durability.